Geophysical surveys are conducted at DoD sites and facilities to search for Target Areas at which munitions were fired or dropped. Surface areas passed over by geophysical detectors, referred to as transects, are usually up to several meters wide, and run in a relatively straight line (as much as terrain permits) from one point of a site to another. When a geophysical sensor system is deployed continuously along transects, anomalous metallic readings may be reported. The Geostatistical Mapping module in VSP allows a continuous estimate of anomaly density across the entire study site to be generated using the surveyed transect data covering only a relatively small portion of the site.
This dialog page contains the following controls (all of these might not be displayed, depending on the contents of your project):
Window Size |
Search window size used to calculate the densities that are used to for the kriging process. See the Window Size discussion below for more details |
Window Size Units |
Units for the search window size. |
Anomaly Proximity Ratio |
How close the anomaly location has to be with respect to the transect center-line in order to be included in the density calculations. The default is 0.5, meaning that the anomaly location has to be located within the bounds of the transect in order to be included in the density calculations. Increase this number to include anomalies that are nearby, but not inside the transect bounds. |
Selected Transects box |
Check the box to select a subset of the transects to include in the density calculations. If the box is unchecked, then all transects are used in the density calculations. |
Selected Transects list |
Highlight the transect data sets that you want to include in the density calculations. |
Include 100% Areas for Variogram Calculations box |
Check this box to include the densities from the 100% Grids in the variogram analysis calculations. |
Include 100% Areas for Kriging box |
Check this box to include the densities from the 100% Grids for the kriging analysis. |
Use Recon Data box |
Check this box to use Recon data instead of geophysical data in the density calculations. |
Recon list |
Highlight the categories of Recon Data that you want to include in the density calculations. |
Calculate Density Estimates button |
Click this button to compute density estimates from the transect and anomaly data, compute an empirical variogram, fit a variogram model to the empirical variogram and then krig the density values over the entire site using the fitted variogram model. |
To use the design, you can simply enter a Window Size value and click the Calculate Density Estimates button. A preview of the kriged data and the variogram model is displayed. If you are satisfied with the results you can press the Apply button to transfer the kriged data to your project. More than likely, you will want to make adjustments on the following pages:
On this page, you can enter the course-over-ground and anomaly data as well as 100% Grid Area boundaries.
On this page, you can view histograms or box-and-whisker plots of the kriged density data.
A circular search window is used to calculate the anomaly density along transects. The diameter of this window is specified by the user. The window is actually a moving window that moves in increments of 1/6 the window diameter along each transect. An example of this is shown in the illustration below. Here, the search windows are centered on the middle transect and proceed along that transect. The anomaly density is computed as the number of anomalies inside the window divided by the area of the transects within the window. The anomaly density of each search window location will be used as input to the geostatistical mapping procedure to estimate the continuous anomaly density over the entire site. If you want to see the anomaly densities that were computed, select Anomaly Densities under the View Settings section of the Layer Control bar. You can export the anomaly density values to a file by right-clicking on the Anomaly Densities setting or from the File / Export menu.
Figure 1 - Search window moving along a transect
Deutsch, C.V. and A.G. Journel. 1998. GSLIB Geostatistical Software Library and Users Guide, 2nd Edition, Applied Geostatistics Series, Oxford University Press, Inc. New York, NY.